The present invention relates to a process for the production of soap from neutral fats.
More particularly, the present invention relates to a process for the direct production of soap from neutral fats having the required concentration of fatty acids, without the intermediate production of a soap having a lower concentration of fatty acids and the subsequent concentration to reach the requested percentage of said fatty acids.
The process according to the present invention is particularly suitable for the direct production of soaps having a high concentration of fatty acids, for example exceeding 63% by weight.
The term xe2x80x9cconcentration of fatty acidsxe2x80x9d, as it is used in the present description and claims, is a conventional way to express the concentration of active fat material which represents in a sense the xe2x80x9cwashing powerxe2x80x9d of a soap.
As it is known, soaps are alkaline salts of higher fatty acids such as oleic, stearic, palmitic and lauric, etc. acids contained in the form of triglycerides in natural fat substances of vegetable and animal origin. They are obtained by reaction of fats and oils with a strong inorganic base, generally sodium hydroxide sometimes substituted or in mixture with potassium hydroxide.
The result of the reaction between neutral fats or oils and alkaline hydroxide is a mixture of soap, glycerine, (residue of the triglycerides splitting in fatty acids), water and all impurities contained in reagents.
According to the known processes, for the elimination of possible impurities, the thus obtained product is subjected to a washing process which is carried out by dilution with water and subsequent separation of the soap by the addition of an electrolyte (NaCl, another salt or sodium hydroxide), being the soap insoluble in electrolyte solutions over a determined concentration. The majority of water soluble impurities and glycerine are eliminated from the soap by the washing waters.
In common processes for the production of soaps, the sodium hydroxide is fed by an aqueous solution and its concentration is generally lower than about 50%; in fact, aqueous solutions having a higher concentration, at room temperature, show an insoluble bottom material. Moreover, with concentrated hydroxide solutions whose limit depends on the kind of fat or oil used, at atmospheric pressure, the saponification reaction does not start up.
With the known processes, the obtained washed soap has a concentration of fatty acids which is not exceeding 62-63% by weight.
In order to obtain a soap with a higher concentration, such as laundry soap, having a concentration of fatty acids of about 72%, or toilet soap, having a concentration of fatty acids of about 78%-80%, it is necessary to subject the saponification product, after washing, to a concentration process.
The concentration process consists in heating under pressure the hot and liquid soap, coming from the washing phase, at about 80-90xc2x0 C. and subsequently in spraying the hot under pressure soap in a vacuum chamber. During this operation, the soap loses part of the water, cooling and concentrating at the same time. When coming out of the vacuum concentration plant, the soap, at atmospheric pressure, is in the form of a plastic mass at a temperature of about 30-40xc2x0 C.
Even though this process is commonly used in industry, it exhibits some drawbacks, which are mainly due to the vacuum itself. In fact, for its processing, the vacuum plant needs a very high vacuum of some mm of Hg, this greatly affects running and ownership costs, moreover it involves operation and maintenance problems.
Another drawback, which is always due to the vacuum concentration process, is the formation of the so-called xe2x80x9cdry specksxe2x80x9d. In fact, during the free expansion of soap, generally going from 2 bars to few mm of Hg, overdried particles of soap called xe2x80x9cdry specksxe2x80x9d are formed conferring the sandy sensation found in some kinds of soap if a proper treatment to remove said particles is not carried out.